1. Field of the Invention
The present invention relates to a centering system for spherical bearings, and has particular utility in connection with spherical bearings that are employed to support the movable exhaust nozzle of rocket propelled vehicles.
2. Description of the Prior Art
Spherical bearings, particularly when exposed to heavy loads and severely hostile environments, tend to function in an improper manner and give rise to problems that degrade the performance of the equipment in which they are employed.
A particular problem or disadvantage of the movable nozzle system of thrust vector control for steering rocket propelled vehicles is the vulnerability of the joint between the static portion, that is the outer race or socket of the spherical bearing that is provided, and the movable portion, that is the inner race or ball thereof, to which the nozzle is fixedly attached. The gases produced by the propellant combustion are very hot in the region of the joint, for example, 4000.degree. to 6000.degree. F., are at substantially the same high pressure as that in the combustion chamber of the rocket motor, and are moving at high subsonic velocities. In order for the nozzle to be moved freely notwithstanding differential expansion of the various nozzle parts adjacent the joint, a clearance space or interstice of about 0.005 inch must be provided between the inner race and the outer race of the bearing, thus providing a crack that hot gases tend to enter. This clearance space is closed by a seal that must be capable of containing the high-temperature high-pressure gases without adding too greatly to the actuation forces that are needed to move the nozzle to steer the rocket vehicle.
Another problem of the movable nozzle system for rocket vehicle thrust control is caused by the heavy "g" loads that are experienced by rocket motors. As a result of such loads, powerful forces are brought to bear on the inner race of the bearing which tend to push it against the side of the outer race. These forces act both laterally and longitudinally with respect to the longitudinal axis of the combustion chamber and nozzle and tend to push the inner race solidly against the side of the outer race and to cause extreme friction between these parts notwithstanding the presence of a lubricant that is provided. Such friction can interfere with proper movement of the nozzle with resultant loss of steering control. There can occur, additionally, misalignment of the center line of the thrust of the nozzle with respect to that of the rocket motor and the center of gravity of the vehicle to which the nozzle is attached. Due to the high thrust output of the nozzle, this can give rise to an undesirable although slight turning moment of the vehicle.
Various proposals have been made in the prior art for overcoming such problems in the application of spherical bearings to the steering mechanisms of rocket propelled vehicles. In my prior U.S. Pat. No. 3,912,172 which is assigned to the assignee of the present invention, there is provided a system for lubricating the spherical bearing to the inner race of which the nozzle is fixedly attached in a manner such that the pressure of the lubricant in the joint is continually related to the pressure in the combustion chamber. The pressure of the lubricant applied to the joint balances or offsets the pressure load on the joint that is exerted thereon by the combustion chamber pressure as the latter acts upon the projected area of the movable nozzle. As a secondary or "back up" system for that just described, the lubricant pressure in the joint is further varied as the width of the clearance space between the inner race and outer race changes due to imbalance of the nozzle load, changes in the clearance space depth being sensed by a movable pin that contacts the inner race.
In U.S. Pat. No. 3,049,887, A. Sherman, also granted to the assignee of the present invention, there is also provided a rocket motor having a nozzle mounted by a spherical bearing. In this patent hydraulic fluid pressure is applied to the clearance space between the inner and outer races for cooling the bearing to keep it from binding and also to cool the congruent interior wall of the nozzle. The fluid is a coolant such as fuel for the motor or a coolant from a separate source.
The arrangements disclosed in the foregoing prior art patents are subject to the possibility of the occurrence of the spherical bearing problems mentioned above in that they provide no means for forcing and maintaining lateral (or axial) centering of the inner race relative to the outer race. The thrust of the disclosure of U.S. Pat. No. 3,912,172 is to balance or offset the pressure load on the bearing joint in the aft direction caused by the combustion chamber pressure acting on the projected area of the nozzle. Pressure of the lubricant applied to the joint will tend to equalize in the clearance space between the inner and outer races, and hence, to be ineffective to offset any imbalance in external lateral, or axial, forces on the inner race of the bearing. U.S. Pat. No. 3,049,877 is concerned principally with cooling the bearing and applies the cooling fluid to the joint in a manner similar to that disclosed in U.S. Pat. No. 3,912,172.
A solution to the above-mentioned problems associated with spherical bearings is provided, in accordance with the present invention, by a system that senses or detects lateral, or axial, displacement of the inner race from a central position with respect to the outer race, and rapidly effects, in a forcing manner, corrective actions as necessary to restore and maintain the inner race in a central position. As a result, the tendency for friction to occur and to interfere with the proper and desired movement of the nozzle is minimized, as is, also, the tendency for misalignment of the center line of the thrust of the nozzle with respect to the center line of the rocket motor and the center of gravity of the vehicle.